Processing @import for arbitrary content

http://stackoverflow.com/questions/17620292/reference-variables-in-a-separate-less-file-using-squishit-support-dynamic-less/17705304?noredirect=1
Merge branch 'master' of https://github.com/PitamberTiwari/SquishIt
rename CurrentDirectory on Asset to ArbitraryWorkingDirectory
change wording from 'dynamic' to 'arbitrary' in less import processing test to avoid confusion